1. Field of the Invention
The present invention relates to a magnetic memory utilizing spin injection magnetization reversal caused by a current, a method of manufacturing the same, and a semiconductor integrated circuit apparatus having the same installed therein.
2. Description of the Related Art
As shown in FIG. 10, a magnetic random access memory (MRAM) in related art as one kind of non-volatile memory using a magneto-resistance effect generally has a structure in which a magnetic tunneling junction (MTJ) element is formed between a write word line 111 and a bit line 113. Here, the MTJ element has a lamination structure including a reference layer (magnetization fixing layer) 121, a tunnel barrier layer 122, and a recording layer (magnetization free layer) 123. Also, the MRAM carries out a write operation by using a magnetic field generated by a current. The two arrows in the figure indicate the magnetization directions of the reference layer 121 and the recording layer 123, respectively. In the MRAM 101 having this structure, when a memory cell is made smaller in order to increase the storage capacity e.g., Japanese Patent Laid-open No. 2005-150482, there is encountered a problem that the magnitude of a reversed magnetic field abruptly increases and the necessary current also abruptly increases with the increase in reversed magnetic field. In addition, when the size of the memory cell becomes equal to or smaller than the 200 nmφ demanded to cause the storage capacity to exceed a gigabit (Gbit), the allowable current density of a wiring is exceeded, and it becomes difficult to write information any more. This is another problem.
On the other hand, spin injection magnetization reversal is known in which magnetization reversal is caused by supporting a polarized spin current (spin injection). This spin injection magnetization reversal has the feature that a current demanded for the magnetization reversal is reduced as the memory cell size becomes smaller. From a viewpoint of this aspect, this spin injection magnetization reversal is suitable for manufacturing a magnetic memory having a high integration level and a large capacity.
In the case of a non-volatile memory using spin injection magnetization reversal (SpinRAM), a wiring dedicated to a write operation using a current (write word line) is not necessary unlike the MRAM (here, indicating a magnetization reversal non-volatile memory by a current). For example, adoption of a structure (On-plug structure) in which a magnetic tunneling junction (MTJ) element 220 is disposed on a plug 231 on a selection transistor 251, as shown in FIG. 11, offers an advantage that a memory cell array can be made smaller. Thus, this On-plug structure is suitable for realizing a high integration level and a large capacity.
Now, a method including processing the overall MTJ at a time is considered as a method of manufacturing the On-plug structure. When reactive ion etching (RIE) is utilized, which is mainly used in the chemical etching processing, a kind of gas corresponding to a material has to be selected because the MTJ element has the complicated material structure. As a result, it is feared that the difficult problem of a tunnel barrier layer (made of an insulator such as Al2O3 or MgO) being damaged by a corrosion gas may arise, so that the characteristics of the MTJ element maybe deteriorated.
On the other hand, the physical etching processing typified by the ion milling is the desirable processing because it is not necessary to select a kind of gas and thus the damage received by the tunnel barrier layer is less. However, under a condition in which a conversion difference due to a shadow effect is reduced (in a region in which inactive gas ions are applied to a wafer in a nearly vertical direction), an amount of reaction product reattached is large, and the reattachment is attached to the tunnel barrier layer. As a result, the MTJ element becomes defective due to a short-circuit caused between a recording layer and a reference layer. This is still another problem.
In order to avoid the above-mentioned anxiety item, as shown in FIG. 12, one process has to be added to the processes in the related art. This process includes stopping the processing for a magnetic tunneling junction (MTJ) element 320 within a tunnel barrier layer 322, and forming a bypass wiring 361 through which a plug 331 and the MTJ element 320 are connected to each other. However, in this case, not only a distance to an adjacent element becomes large, so that a photo resist process allowing the alignment to be made with high precision is demanded, but also an actual cell size becomes larger than an ideal one. As a result, it becomes difficult to realize the large capacity due to the high integration.